Due to its inert properties, nitrogen gas has long been a widely used industrial gas. Industrial applications have included packaging of perishable foods and blanketing of such foods in storage, provision of none explosive atmospheres and reducing atmospheres for soldering and brazing, and purging of explosive gas atmospheres from tanks and pipes prior to welding operations.
Traditionally, nitrogen has been produced by distillation of liquified air, and has been provided to industrial users in high pressure canisters. Typically, these canisters are large and heavy. While nitrogen gas is generally readily available and inexpensive, transportation, storage and rental of nitrogen gas containers can be costly for the industrial user. Also, there is always some danger associated with transportation and handling of high pressure gases. In applications where nitrogen gas must be used in remote locations, the danger, cost and inconvenience of transporting and handling large, heavy, high pressure containers is compounded. An example of such situations is the on site repair of refrigeration systems during which nitrogen gas may be used for purging of refrigeration systems before brazing operations, charging systems for leak checking, and for breaking vacuums in large chillers.
Recently, nitrogen gas has bee produced utilizing selectively permeable membranes, such as membranes developed by Dow Chemical Company. To produce nitrogen gas, pressurized air is passed through thin hollow fibers fabricated of the selectively permeable membrane material, oxygen, water and other gases permeate through the membrane wall of the fibers more rapidly than nitrogen, leaving a stream of substantially pure nitrogen after flowing a sufficient distance through the fibers.
This method has been used to produce nitrogen on an industrial scale for subsequent distribution in traditional, high pressure canisters. More recently, membrane nitrogen systems have been available for on site installation by industrial users of nitrogen gas. These systems are generally large and operate upon compressed air available from plant systems on location or separate dedicated compressors. Smaller units have been available for specialized applications, such as blanketing aircraft fuel tanks, and have relied upon local sources of compressed air, such as bleed air from a turbine engine compressor.
No system of the prior art has provided a complete, compact, readily transportable, safe nitrogen source which can provide substantially pure nitrogen for general purpose use at remote locations.